All organisms are made of cells. In the hierarchy of biological organization, the cell is the simplest collection of matter that can be alive. Indeed, many forms of life exist as single celled organisms. More complex organisms, including animals, are multicellular; their bodies are cooperatives of many kinds of specialized cells that could not survive for long on their own. Even when cells are arranged into higher levels of organization, such as tissues and organs, the cell remains the organism’s basic unit of structure and function.
In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction .The cell was first discovered by Robert Hooke in 1665, which can be found to be described in his book Micrographia. Hooke discovered a multitude of tiny pores that he named “cells”.
However, Hooke did not know their real structure or function. With microscopes during this time having a low magnification, Hooke was unable to see that there were other internal components to the cells he was observing. Therefore, he did not think the “cellulae” were alive. Anton van Leeuwenhoek is another scientist who saw these cells soon after Hooke did. He made use of a microscope containing improved lenses that could magnify objects almost 300-fold. Under these microscopes, Leeuwenhoek found motile objects and stated that motility is a quality of life ,hence these were living organisms.
Later advances in lenses, microscope construction, and staining techniques enabled other scientists to see some components inside cells. Eventually the cell theory was later formulated in 1839. This is usually credited to Matthias Schleiden and Theodor Schwann. But they proposed spontaneous generation as the method for cell origination, but spontaneous generation (also called abiogenesis) was later disproven. However, many other scientists like Rudolf Virchow contributed to the theory stating all cells only arise from pre-existing cells and made important contributions to this theory.
Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells.
- All living things are composed of one or more cells.
- The cell is the basic unit of life.
- New cells arise from pre existing cells.
The expanded version of the modern cell theory can also include:
- Cells carry genetic material passed to daughter cells during cellular division.
- All cells are essentially the same in chemical composition.
- Energy flow (metabolism and biochemistry) occurs within cells.